Forest Ecosystem Monitoring Research Articles

Litterfall and Leaf Area Index in the CONECOFOR Permanent Monitoring Plots

Forest canopies are more sensitive and react more promptly to abiotic and biotic disturbances than other stand structural components. Monitoring crown and canopy characteristics is therefore a crucial issue for intensive and continuous monitoring programs of forest ecosystem status. These observations formed the basis for the measurement of annual litter production and leaf area index (LAI) in the Italian permanent monitoring plots (CONECOFOR program) established within the EC-UN/ECE program "Intensive Monitoring (Level II) of Forest Ecosystems". Preliminary results after three years of observation are presented. The low value of within plot mean relative standard deviation (20.8 ± 1.9%) of litter production, which in any case never exceeded 30%, accounted for the good sampling error and accuracy of the chosen method, which seems to be accurate enough to detect changes in litter production through the years. The higher inconsistency of the amount of woody and fruits fractions over the years demonstrated the greater reliability of leaf fraction or, on the other hand, of LAI compared to total litter. Mean values of annual leaf-litter and total litter production and LAI were rather high in comparison with data reported in literature for similar stands, and reflected both a medium-high productivity and a juvenile phase in the development of the selected stands on average. Focusing on changes in litter production through the years, statistical analysis on a sub-sample of plots showed the existence of significant differences both in leaf litter and total litter production. These findings seem to attribute to the "year" factor a driving role in determining changes in litter production and LAI. Temporal intermittence in data collection, together with the shortness of the monitoring period, make it difficult to speculate or arrive at definitive conclusions on changes in litter production due to time-dependent factors. The importance of having a complete database to increase index representativeness and reliability and, on the other hand, of performing an integrated results analysis which takes into account the outcomes of other research actions, is recognized as an indispensable requirement for achieving the goals of the monitoring program.

The Integrated and Combined (I&C) evaluation system to detect status and trends of the CONECOFOR Permanent Monitoring Plots

CONECOFOR is the Italian program for the intensive monitoring of forest ecosystems sponsored by the Ministry for Agricultural and Forest Policy and the European Commission. It is based upon a series of investigations carried out on 20 (27 from 1999) plots located throughout Italy. The investigations collect data on various ecosystem compartments (soil, ground vegetation, trees, atmosphere) and processes (atmospheric inputs, tree nutrition and growth). A major benefit of intensive monitoring programs is the opportunity they provide to organize integrated studies aimed at understanding the driving forces acting at the ecosystem level. In Italy, the Integrated and Combined (I&C) evaluation system within the CONECOFOR program involves three major approaches: (i) the evaluation of risk status in relation to air pollution, (ii) the quantification of the ecosystem’s status and changes, and (iii) the evaluation of the relationship between pressure and status indicators through time. The I&C project involves scientists from many institutions; major emphasis is placed on the evaluation of data quality and precision. These are regarded as the basic steps in the whole project and a likely source of information about the suitability of the current sample sizes for providing a proper estimation of the parameters under consideration. The paper will provide information on the conceptual and methodological background of the I&C project

Ozone and nitrogen dioxide measurements in the framework of the National Integrated Programme for the Control of Forest Ecosystems (CONECOFOR)

Ozone (O3) concentrations were monitored using passive (diffusive) samplers at 20 permanent monitoring plots of the National Integrated Programme for Forest Ecosystem Monitoring (CONECOFOR) during late spring and summer from 1996 to 2000. Nitrogen dioxide (NO2) concentrations were measured at the same sites with passive samplers during the same months in 1999 and 2000. Measurement devices were placed at a short distance from the forest plots in areas with freely circulating air. The exposure period for O3 passive samplers was 1 week; NO2 samplers were exposed for 7 days in 1999 and 14 days in 2000. Mean O3 concentrations recorded by the passive samplers for the monitoring periods in individual years vary from 75.2 to 125.8 μg m-3, showing considerable differences between individual years and the geographical locations of the monitoring sites. Generally speaking O3 concentration levels are higher at the plots located in Central and Southern Italy. The highest mean weekly concentrations were recorded in Sicily with a maximum of 171 μg m-3. No correlation can be found between O3 levels and elevation if all the plots are considered, while a significant increase of O3 levels with elevation can be observed in the six plots located in the Alpine region. The correlation analysis of 5-year mean concentration data and plot latitude show a moderately close relationship. Mean weekly concentrations often exceed 65 μg m-3 as 24 h mean, one of the short term thresholds proposed for the protection of vegetation. Exceedances are recorded in all monitoring periods. At the permanent monitoring observation plot in Sicily this threshold was exceeded in all the years of the study. Mean weekly or fortnightly NO2 concentration levels are generally very low, with the exception of some plots influenced by nearby emissions or transport phenomena. NO2 probably exceeds the critical level for the protection of forest ecosystems at one plot only. No correlation was observed between NO2 and O3 concentration data.

Long-term ecological research on Italian forest ecosystems: perspectives and conclusions

The paper summarises the contents of the present volume devoted to forest research in Italy, within the National Programme for Forest Ecosystem Monitoring (CONECOFOR), part of the Level II forest monitoring, and other linked regional and provincial monitoring activities. The coordination of the project, through a National Focal Centre and a Task Force for the Integrated and Combined Evaluation of results, made up of the foremost Italian experts working in the field, is outlined. No clear signals of strong negative impacts emerge from the papers, although the results of several studies indicate nitrogen and ozone as possible causes of disturbances in a number of plots. The effects of the deposition of acidity are largely buffered by the nature of the soils, while nitrate is leached from the plots where runoff is analysed, indicating N saturation of soils. This paper describes the main activities of the Task Force as regards data validation and elaboration, aimed at providing reliable information leading to sustainable forest management in Italy as well as making a useful contribution to international activities in a Pan-European context.

Intensive monitoring of forest ecosystems in Europe: 2: Atmospheric deposition and its impacts on soil solution chemistry

In order to gain a better understanding of the effects of air pollution and other stress factors on forests, a Pan-European programme for intensive and continuous monitoring of forest ecosystems has been implemented in 1994. Results of this intensive monitoring programme presented in this paper are related to the surveys on atmospheric deposition and soil solution chemistry, focusing on data for 1997. Both bulk deposition and throughfall of N was higher than that of S at nearly all the plots, especially in Western Europe. The average calculated total N deposition was approximately twice as large as S. Approximately, 55% of the considered plots received an N input above 1000 mol c ha −1 yr −1 (14 kg ha −1 yr −1), being a deposition level above which the species diversity of the ground vegetation may decrease. The total input of acidity ranged mostly between 200 and 4000 mol c ha −1 yr −1. The deposition of SO 4, NO 3 and Ca was significantly higher in the central/eastern part of Europe, but NH 4 was slightly higher in western Europe. A highly significant positive correlation of atmospheric deposition and rainfall was observed for most ions. The concentrations of NO 3 in soil solution exceeded the EU ground water quality criterion of 800 mmol c m −3 in the subsoil at 9% of the plots. Al/(Ca+Mg+K) ratios exceeded a critical ratio of 1.0 in approximately 30–39% of the plots, depending on the layer considered. The concentration of potentially toxic Al in the subsoil was strongly related to the concentration of SO 4 and NO 3 in soils with a base saturation below 25% or a pH below 4.5, indicating that Al release is the dominant buffering process in acid soils. Above a base saturation of 25% and a pH level of 4.5, there was a strong relationship between Ca and strong acid anions, indicating that the acidity is mainly neutralised by the release of base cations in less acidified soils. The variation in concentrations of major ions in the soil solution could be, to a large extent, explained by differences in atmospheric deposition and meteorological conditions.

Intensive monitoring of forest ecosystems in Europe: 1. Objectives, set-up and evaluation strategy

In order to contribute to a better understanding of the impact of air pollution and other environmental factors on forest ecosystems, a Pan-European Programme for Intensive and Continuous Monitoring of Forest Ecosystems has been implemented in 1994. Results of the Programme must contribute to a European wide overview of impacts of air pollution and the further development of its control strategies, being described in air pollution protocols. Objectives of the Intensive Monitoring Programme related to air pollution are the assessment of: (i) responses of forest ecosystems to changes in air pollution; (ii) differences between present loads and critical loads (long-term sustainable inputs) of atmospheric deposition; and (iii) impacts of future scenarios of atmospheric deposition on the ecosystem condition. Furthermore, the Intensive Monitoring Programme contributes to the assessment of ‘criteria and indicators for sustainable forest management’, such as the maintenance of forests as a net carbon sink to reduce the build up of atmospheric greenhouse gasses and the maintenance of species diversity of ground vegetation. The Intensive Monitoring Programme, which is carried out on approximately 860 selected plots, comprises monitoring of crown condition, forest growth and the chemical status of soil and foliage at all plots and monitoring of deposition, meteorology, soil solution and ground vegetation in a subset of the plots. In order to meet the major objectives of the Intensive Monitoring Programme, studies have been or are presently carried out with respect to the assessment of: (i) correlations between site and stress factors and the “forest ecosystem condition”; (ii) trends in stress factors and/or ecosystem conditions; (iii) critical loads, by evaluating the fate of atmospheric pollutants in the ecosystem with input–output budgets; and (iv) large-scale and long-term impacts of climate and deposition on forests and vice versa. Examples of those studies are given and the potential of the Programme to fulfil the objectives is evaluated.

The significance of different indices for stand structure and diversity in forests

Data from the so-called Level II Plots which were established within the frame of the Pan-European Programme for Intensive and Continuos Monitoring of Forest Ecosystems were used to quantify stand structure and species diversity by means of different indices. The calculations presented are based on species composition, spatial pattern as well as diameter and height distribution. The data assessed are suitable to calculate different measures of structural diversity, if a mapping of the stands is carried out. A comparison of the different indices by means of correlation analysis shows that there exist only few and weak correlations between species diversity of different vegetation layers, and between plant species diversity and diversity of stand structure, while among all the indices of stand structure a correlation exists. More complex indices of stand diversity perform quite well in characterising the specific situation. Mountain forests are compared with forests from lower elevations. They show a tendency towards irregular stand structures. No correlation between the naturalness of tree species composition and the calculated diversity indices can be found within the sample.

Crown defoliation improves tree mortality models

The objective of this study was to evaluate the predictive power of crown defoliation, assessed in 5% classes, in predicting year-to-year tree mortality. A visual analysis of Swiss Forest Health Inventory (SFHI) data suggested an exponential increase in the mortality rate with increasing defoliation. We verified this trend using a logistic regression model with defoliation, social position and their interaction as explanatory variables. We fitted our model to SFHI data for the years 1990–1997 (annual mortality rate=0.32%), and validated the model with data from long-term forest ecosystem monitoring sites for the years 1995–1998 (annual mortality rate=0.48%). Several indicators of prediction accuracy showed that regression models with total defoliation achieved 40–50% higher accuracies than models with unexplained defoliation, i.e. the portion of defoliation that field crews are unable to attribute to known causes. The logistic regression model with total defoliation correctly predicted 33% of the dead trees in the calibration data set, and 57% in the validation data set. This prediction accuracy was calculated with a deterministic method, using a predicted threshold probability above which trees were assumed to die. Our study suggests that including defoliation has the potential of considerably improving the prediction accuracy of models that predict tree mortality based on competition indicators and tree size alone.

Interpolation of Daily Global Solar Radiation with Thin Plate Smoothing Splines

Thin plate smoothing splines incorporating topographic dependence were used to interpolate daily global solar radiation in the Bavarian forest ecosystem monitoring network, with the degree of data smoothing determined by minimizing the generalized cross validation. A simple cross validation method was used to discuss the spatial distribution of mean relative errors at 18 forest climate stations. The results show that, from this network 14%–30% mean relative errors can be expected for most of these forest climate stations in summer, and 20%–30% mean relative errors can be found at a few of forest climate stations in winter. Time-averaging can reduce these interpolation errors. In this network a mean relative error of 10% can be expected for weekly and biweekly mean solar radiation at most of forest climate stations in summer. Large errors are related to low radiation amount under heavy cloud cover. Mean relative errors increase as daily global solar radiation decreases.

Heavy metals (Cd, Cu, Zn) in wood and wood-feeding insects and other invertebrates associated with decaying pine trees.

The study of metal distribution in trees and wood-feeding species of invertebrates is of interest from the perspective of ecological risk assessment of metal pollution as well as of forest ecology in general. Wood-feeding invertebrates are important for the physical destruction and natural removal of dead trees in forests. By carrying with them a microbial complex of wood-decompos ing fungi, bacteria, protozoa, and yeasts, they contribute to the chemical process of wood decay (Ausmus 1977; Mamaev 1977). The dynamics of wood decomposition keep up energy flow and matter circulation in forest ecosystem, which are crucial in sustaining a high biodiversity in forests. At the same time, species of bark- and wood-boring beetles have been shown to accumulate heavy metals in their body tissues according to the degree of industrial pollution of the environment (Vogel 1986; Heliovaara et al. 1987; Rothz-Holzapfel & Funke 1990; Esenin 1990). As forest insects and other invertebrates function as food items for birds and mammals they are linked to the process of foodchain transfer of metals in contaminated environments. The present study investigates the use of xylobiont invertebrates as components of a multi-species indicator system for the monitoring of forest ecosystems under metal stress. The approach followed in this study is based on the principle that each stage of decomposition of tree trunks, as shown by changes in density, hardness and chemical composition of the wood, is associated with a particular assemblage of insects and other wood-feeding invertebrates (Schimitschek 1952,1953; Mamaev 1977). The study has been carried out in two pine forest areas in The Netherlands, with different levels of metal contamination. One area, situated near the township of Budel, has been polluted by past emissions from a nearby zinc smelter; the other, a less polluted site, was situated near the city of Arnhem at about 100 km north-east of Budel. Metal contamination levels of soil and fauna of the two areas have been described earlier (Ma et al.1991). Several of the species of bark- and wood-feeding insects mentioned in this paper are studied for the first time in ecotoxicologi cal research.

Field aspects of line intersect sampling for assessing coarse woody debris

Due to modern forestry practises, the amount of coarse woody debris has decreased considerably in Swedish forests. Since many threatened species depend on this substrate, assessment of it is central in the monitoring of forest ecosystems. The plot-based methods normally used for timber cruising tend to be inefficient when the objects of interest are sparse and, consequently, line intersect sampling is an interesting alternative for assessing coarse woody debris on the ground. With this method there is a risk that the surveyor, without being conscious about it, tends to move towards or away from a log instead of following a straight line. The result is biased estimates. In this paper, a field test concerning the surveyors' influence on estimates is presented. Line intersect sampling for assessing coarse woody debris was tested by 11 surveyors in four old conifer stands in northern Sweden. The study did not indicate any systematic differences between surveyors in their way of performing the inventory, although for the surveyors as a group a negative bias was found. The bias was, however, only due to a large underestimation in one single stand, meanwhile the measurements in the other stands were close to reference values. Random measurements errors are, however, likely to be introduced. The conclusion is that systematic errors should not be a major problem in line intersect sampling but that the dimensioning of surveys should consider the random error component introduced by surveyors.

Potential and limits of NOAA-AVHRR temporal composite data for phenology and water stress monitoring of temperate forest ecosystems

We focussed on the potential and limits of NOAA-AVHRR 5-day composite data for monitoring the phenology and the fluxes of temperate forests at regional scale. The spatio-temporal variability ofkm2 Normalised Difference Vegetation Index (NDVI) was large, and primary varied with the deciduous/ coniferous mixture. It could provide the phenological cycle of deciduous ecosystems. For the large coniferous Landes forest, it characterised the different ecotypes, and was sensitive to land use (age of the pine stands) and understorey vegetation. Relationships between NDVI, TS and rainfall confirmed the ability of km2 thermal infrared data to infer the water status of this forest.

Natural organic matter contribution to throughfall acidity in French forests

This study examined the natural organic acidity of throughfall in French forests in order to determine the natural and anthropogenic contributions to the total acidity. The first results presented here were achieved from 64 open field precipitation and throughfall samples, collected from June to December 1996 at 7 RENECOFOR stations (French permanent plot network for the monitoring of forest ecosystems). A titration method was developed to quantify the organic contribution to the acid neutralizing capacity (ANC), to the charge balance and to the weak acidity. The natural organic acids occurring in throughfall samples were characterized by a mean site density of either 7.3 or 10.2 μeq/mg of C, considering only titratable organic acidity or total organic acidity, respectively. The mean charge density was 5.2 μeq/mg of C and, as a linear relationship exists between the charge density and pH, an estimate of the organic anion concentration can be obtained directly from dissolved organic carbon (DOC) and pH measurements. The organic contribution to the ANC, and thus to the buffering capacity, is of prime importance for those waters which have pH values between 3.8 and 6.6, and characterized by a low bicarbonate content and a high DOC concentration. The mean organic contribution to the titrated ANC was 2.2 μeq/mg of C, which is less than half the charge density. These first results show that the acid-base properties of DOC are similar for all studied samples, despite different geographical situations, climates, and vegetation types. Furthermore, when comparing these results to literature data (obtained for stream, lake, and soil solution samples), it appears clearly that, unless a methodological artifact exists, the organic acids dissolved in throughfall are weaker.

Theoretical and practical criteria for the selection of ecosystem monitoring plots in Swiss forests

A great deal of attention has been paid to the selection of nature reserves. These are important from a conservation viewpoint but, for long-term evaluations, it is important to monitor ecosystems. The need for long-term monitoring plots has been recognized for some time in forest ecology. Of the natural ecosystems, forests are some of the most difficult to monitor because of the time-scales involved in the life-spans of the dominant organisms (100 → 1000 years). The selection of long-term forest ecosystem monitoring plots is a critical process involving decisions that need to remain valid for many years. Traditional sampling theory suggests that some form of systematic or random sampling may be appropriate, but this is usually inappropriate for the selection of ecosystem monitoring plots. Instead, the selection of plots more closely resembles some of the procedures that are used in the selection of nature reserves. In Switzerland, a monitoring programme has been established which uses a number of criteria for the selection of sites. These include site homogeneity, the abundance and sensitivity of the plant communities to change and the presence of pre-existing data series or monitoring equipment. In addition, the human factor is incorporated by selecting sites from throughout the country, with the willingness of the local forest managers to help with the project being an important factor influencing the final choice of plots. In contrast to most inventories, statistical representativeness is not a requirement for the programme, as the plots are treated as a series of case studies.

Monitoring of forest ecosystems in the Russian Subarctic: effects of industrial pollution

Results of long-term investigations carried out in the vicinity of large nickel enterprises in the Russian Subarctic are presented. Levels of air, precipitation, soil and vegetation pollution were estimated and zones of varying degrees of damage to forests as a result of industrial impact were determined over the area of the Kola peninsula. In the Norilsk region, these investigations are now in progress. For the Kola peninsula, the industrial impact on forests is generally restricted to a distance of 30 km from the emission sources. The highest levels of contamination are observed in the area adjacent to smelters. Methods for monitoring are discussed and the data on the response of coniferous trees to different levels of environmental pollution are presented.

Forest mapping from multi‐source satellite data using neural network classifiers—an experiment in Portugal

Abstract The monitoring of forest ecosystems and their biodiversity is a major challenge for satellite remote sensing. The opportunity now exists for operationally using multi‐sensor high resolution satellite data from optical, infrared and microwave parts of the electromagnetic spectrum. An experiment is reported on the integrated use of Landsat Thematic Mapper (TM) imagery combined with ERS‐1 Synthetic Aperture Radar (SAR) imagery for mapping eight identifiable types of forest ecosystem in a test area of approximately 100 x 100 km in western central Portugal. The TM and SAR images were geometrically co‐registered and resampled to a spatial resolution of 25 m. The SAR data were despeckled using a multiple regression method based on the TM scene. The classification of the integrated multi‐sensor dataset was carried out using multi‐layer perceptron neural networks which were trained using ground truth samples taken from test sites within the experimental area. The neural network was used in two separate mapping stages: the first to map nine basic classes of land cover including one of forest, and the second to map eight different types of forest within the generic forest land cover area. The total classification accuracy achieved for the eight forest classes was 77.7% from the integrated TM and SAR dataset, which was 1.7% higher than the accuracy achieved using the TM data alone. Whilst the overall classification accuracy did not improve significantly through the use of SAR data in addition to TM, there were some significant gains for certain individual classes. In particular, the addition of the SAR channel gave a 13.1% improvement in the discrimination of a mixed conifer/broad‐leaf class largely by giving better separation from a pure conifer class.

森林生態系モニタリングの地域ネットワーク化をめざして : 「森林生態系のモニタリングを考える研究集会」開かれる

森林生態系モニタリングの地域ネットワーク化をめざして : 「森林生態系のモニタリングを考える研究集会」開かれる

Monitoring of coniferous forest ecosystems in Sweden.

Monitoring of coniferous forest ecosystems in Sweden.